The invention relates to a device for cutting sheets of wood off square timber without forming chips, said device comprising a machine frame and a feeding device, which conveys the square timber in the longitudinal direction against a cutter blade, slanted at an angle to said square timber, with a pressure bar, which is located at a distance from the cutter blade and is attached to a wood guide surface.
It is well-known to use, instead of the sawing method, the cutting method (DE-A-37 02 909), which does not form chips and thus functions virtually without a loss, in order to produce sheets of wood from a square timber. It is also well-known to adjust in the case of a device of the aforementioned class (DE-A-40 26 346) the thickness of the sheets of wood produced or the thin boards by changing the distance between the cutter blade and the adjacent pressure bar by means of a setting mechanism. In the prior art device this distance is set as a function of the result of the measurement of the square timber prior to each cutting operation. With this known device the thickness of each individual sheet of wood that is produced can be influenced; however, the taper cannot be influenced.
In everyday operations, however, there is a need to influence precisely the taper of the sheets of wood, which are produced, in the transverse direction, in order to compensate for a variation in thickness between both longitudinal edges of the sheet of wood.
Such a difference in the thickness of the sheet of wood in the transverse direction also occurs when the cutter blade is arranged exactly parallel to the wood guide surface. Since the sheet of wood to be cut during the cutting operation is compressed between the cutter blade and the pressure bar, which is rigidly attached to the wood guide surface, the compressibility of the wood, which is usually cut in the moist state, affects the resulting thickness of the sheet of wood.
The compressibility depends, however, on the growth ring arrangement in the cross section of the wood, and in particular, the angle at which the growth rings run with respect to the surface of the sheet of wood. Owing to the approximately circular pattern of the growth rings in the cross section of the trunk, this angle of the growth rings relative to the surface of the sheet of wood varies over the width of said sheet of wood. The result is that in most cases the thickness of the two longitudinal edges of the sheet of wood that is produced varies immediately after the cutting operation, a state that is called "taper in the transverse direction".
In the known device (DE-A-40 26 346) the setting of the cutter blade is controlled in such a manner as a function of the measured thickness of the square timber that the waste sheet, remaining after the last cutting operation exhibits, the same thickness as the other sheets of wood, thus maintaining a specified tolerance. If, however, the square timber is cut conically as a consequence of the varying compressibility in the transverse direction, these conical variations can add up in the many successive cutting operations in such a manner that the resulting waste sheet exhibits such a severe taper in the transverse direction that it is not suitable for further processing, even though its thickness is still within the permissible tolerance.
In another known device (DE-A-39 26 396) the pressure bar opposite the cutter blade is pivot-mounted on the wood guide surface. However, the pivoting motion takes place around a swivel axis, which extends in essence parallel to the cutter blade. Such a pivotability is not provided and also not suitable for compensating a taper of the square timber, especially since there is no relative adjustment between the wood guide surface and the cutter blade. Thus, in this device only the pressure conditions over the entire length of the cutter blade change uniformly. However, the thickness and/or the taper of the sheets of wood produced is not affected.
Therefore, the object of the invention is to design a device of the aforementioned class in such a manner that an error in taper resulting during the cutting operation can be automatically compensated.